1. Field of the Invention
This invention relates to a process for the production of aromatic aldehydes.
2. Description of the Prior Art
Aromatic aldehydes, particularly representative of which is benzaldehyde, find widespread usefulness as intermediates in the manufacture of perfumes, dyes, drugs and like specialty products. The prior art method for the production of benzaldehyde for the foregoing uses involves the chlorination of toluene followed by the hydrolysis of the resultant dichlorinated derivative. This method is beset with difficulties which translates to the fact that it is a relatively costly way of producing this intermediate.
Recently, investigative interest has centered on potential ways for producing styrene from toluene because of the increasing availability of toluene as opposed to that of benzene and the ever mounting cost of ethylene. An applicable route of this nature involves the conversion of toluene to benzyl alcohol followed by a homologation step to provide phenethanol which upon dehydration yields styrene. The most refractory reaction in the sequence is the conversion of toluene to benzyl alcohol. This conversion can be fairly readily achieved by acetyloxylating toluene followed by hydrolysis but at the considerable sacrifice of introducing highly corrosive acetic acid into the reaction system.
The direct oxidation of toluene to benzyl alcohol has to date proven to be an elusive desideratum insofar as the oxidation reaction is essentially completely selective toward the formation of the aldehyde. Accordingly, one is constrained to hydrogenate the aldehyde in order to obtain styrene ultimately which procedure nonetheless augurs to be an overall improvement over the acetyloxylation route.
As indicated previously, the method of producing benzaldehyde via the chlorination of toluene is costly and thus economically unacceptable for any scheme in deriving therefrom a commodity chemical such as stryene. The direct oxidation method, while potentially attractive, has long suffered in practice because all of the catalysts purported to be useful for this purpose provided unacceptively low selectivity and conversion. However, a noteworthy advance in this area of technology was to be found in U.S. Pat. No. 3,579,589. Therein it is essentially taught that a combination or uranium and molybdenum oxides represent an effective catalyst system for conversion of toluene to benzaldehyde. The object of this invention is that of modifying the aforesaid catalyst system with a promoter metal so as primarily to enhance substantially the selectivity characteristics thereof.